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That Was the Year that Was

Homebuilt reflections: Three steps forward, two-and-a-half back.

I am writing this on Dec. 31, 2014. On this day some people prepare resolutions. I catalog regrets.

At this time a year ago I was racking my brain over an apparent rise in oil temperature in my homebuilt, which has an updraft-cooled Continental TSIO-360 engine. This is an airplane I designed and built and that I spend a few hours each week coaxing toward perfection, not that it’s in any danger of getting there.

Several years ago I had a long struggle with elevated oil temperature. I eventually concluded that air going to the oil cooler was stopping for a chat with the exhaust pipes, and possibly even with the turbocharger, on the way. By the time it reached the oil cooler its temperature was already around 140 degrees Fahrenheit.

I resolved this problem by building a duct that picked up air inside the cowling below the exhaust pipes, where I thought it ought to be cooler, and delivered it to the oil radiator. This seemingly solved the problem; the oil temperature dropped from 210 degrees to the recommended 170, and I stopped paying attention to it.

But now it was misbehaving again.

While trying to understand what could have changed, I addressed myself to another irritation. Friction in the pitch control system had increased, and was not linear; it had a “bump” in the middle. Nearly all of the friction had to be coming from the 10-foot-long piano hinge connecting the elevator to the stabilizer and serving, incidentally, as a gap seal between them. I had done my best to make that hinge perfectly straight when I built the plane — that particular part had been done around 1984 — but I knew it wasn’t perfect because I had had to use a drill motor to spin the hinge wire into it. That imperfection, I thought, together with dirt and lack of lubrication, was the problem.

So I got my next-door neighbor, John Biggs, who masters an array of weird craftsmanly skills, to braze a 0.098 reamer onto the end of a 6-foot piece of 0.096 drill rod. When I began to feed the WLR — the world’s longest reamer — into the hinge, it quickly bogged down in black gunk, and I concluded that I would have to take the elevator off, ream the two halves of the piano hinge separately while inundating them in WD-40, and then put them back together for a final pass (or two or three).

In the meantime several people were telling me that this was a fool’s errand. Because the stabilizer flexes in flight, the hinge line would never be straight, and so the resistance would always be there. Discouraged by this advice, although I did not entirely concur with it, and because taking the elevator off is a two-person job and I didn’t have a second person handy, I allowed myself to be diverted into a third activity, namely that of reversing the position of the engine’s intake manifold.

This was a project that I had been talking about for years. Finally a reader of my blog about the airplane taunted me with being all talk and no action. Thus goaded, I got out my hacksaw.

The idea was to put the throttle body on the cold side of the baffles. Normally, the throttle body and fuel controller on this engine are located on top, near the front, where they are bathed in cold air in the typical downdraft-cooled installation. In my airplane, however, they were in engine-heated air, and, besides, the intake manifold was blocking the way of air trying to get to the cowl exits.

This project occupied me, and grounded the airplane, from February through much of May.

I thought it looked pretty cool when it was done. Nearly all the clutter on top of the engine was gone, and air now had a clear path to the outlets. Fuel, on the other hand, had to make a detour, since both the fuel pump and the injector distributor are at the front of the engine but the fuel controller/air throttle is now at the back. But it was all plumbed with neat parallel stainless-steel lines that were nice to look at, as was the big aluminum duct running from the turbocharger to the throttle body. You develop a sense of the aesthetics of engines by working on them.

The change actually did seem to result in smoother running during long periods of idling on the ground. But it had no discernible effect on performance, and it messed up the mixture distribution, which had previously been very nicely optimized with GAMI injectors that allowed me to run smoothly far lean of peak. It has been a slow process, still not finished, to get all the cylinders to hit peak EGT again at more or less the same time.

All along, I had been tormenting myself about the oil temperature. In January I took the oil cooler to Pacific Oil Cooler, half an hour away, where workers pumped solvent back and forth through its galleries for days until the liquid came out looking like a decent Sauternes. That did not help. I calibrated probes, performed a messy autopsy upon an oil filter in search of any telltale glitter that might suggest a spun or ­disintegrating bearing, and checked ­compression hot and cold for any suggestion of worn piston rings. Nothing.

In midsummer I instrumented the oil cooler air duct, using a device intended for backyard chefs that transmits temperatures from two probes by radio to a remote indicator. With an OAT at altitude of 75 degrees, the temperature on the “cold” side was 120 degrees and on the hot side 180. Evidently the air entering the duct was still being preheated by the exhaust pipes.

On the basis of some theories about what air entering the cowling must be doing, I installed a vane in the left side of the cowling air inlet. Its purpose was to cause cool inlet air to follow the inner wall of the cowling, from which I suspected it was separating, on its way to the oil cooler duct inlet, so that it would not visit any exhaust pipes on the way. This was a success; the cold-side temperature dropped by 25 degrees and the temperature rise across the cooler increased by 20, to 80 degrees. One day in September I even saw 90. But the oil temperature still refused to drop back to 170.

It was in September that I got the idea that all this trouble might be based on a silly error. A single instrument on my panel displays either oil or induction air temperature (induction air is heated while being compressed by the turbocharger, and it is sometimes useful to know how much). I had never gotten around to labeling the selector switch, and now I suspected that when I believed the oil temperature was 170 I had really been looking at the air temperature. I searched back through photographs from the past few years in which the instrument panel was visible. Sure enough, the toggle switch was in the wrong position. Sheesh. I had been wondering why the induction air temperature was so high.

Late in the year I decided that, even though I never fly at night anymore, the plane ought to have a landing light — it has nav lights, panel lights and blinking anti-­collision lights — just for the sake of completeness. I consulted my old friend Peter “I’ll fly anything” Lert, a polymath who can provide reliable counsel on any topic from the proper intonation of Old High German liturgical chants to the best O-ring formulations for trash compactors. He pointed out a suitable bank of high-intensity LEDs, intended for night off-road racing through Baja and that sort of thing, in the JC Whitney catalog, definitely not FAA approved, for $40. One of the joys of homebuilding is two-digit prices.

With the cool weather the oil temperature has come down a bit, so I can stop thinking about it for a while. Now I really need to deal with that piano hinge.

For more articles from Peter Garrison’s Technicalities column, click here.

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